The invention relates to a process for manufacturing a one-piece cooling-channel piston and a piston in accordance with the primary claim of the independent patent claims.
From DE 44 46 7216 A 1 a process is known for manufacturing a one-piece cooling channel piston, in which a piston blank is produced by forging and an ring-shaped recess is introduced between a piston crown and the attached piston skirts by machining. Then an open-bottomed cooling channel is created in the piston crown by machining. After this, the wrist pin bores are created and the outside contour of the piston is machine finished. Following these steps the cooling channel, which is still open to the bottom, is closed by a cover ring so that the cooling medium circulating in the cooling channel (specifically engine oil) remains in the cooling channel to cool the piston crown.
As part of this process for manufacturing the cooling channel piston it is necessary that the axial height of the ring-shaped recess be at least equivalent to the axial height of the cooling channel. Because of the gap between the piston skirts and the piston crown (also called the piston top), undesirable instability results during operation of the cooling channel piston, the consequence of which is that the guidance of the cooling channel piston within the cylinder is inadequate.
The object of the invention is therefore to propose a process for manufacturing a one-piece cooling channel piston and a piston by which the said disadvantages are eliminated.
Under the invention it is envisioned that a component is welded on below the piston ring belt, extending the piston ring belt. This component supplements the guidance surface area, where the entire guidance surface area now consists of the surfaces of the component and also of the piston skirts. The guidance surface area is increased overall, so that instability in the cooling channel piston is eliminated, since the component contributes to rigidity, and the operating characteristics of the cooling channel piston inside the cylinder are considerably improved. The geometric dimensions of the component, specifically the axial extent between the piston crown (piston top, specifically the lower edge of the piston ring belt) and the upper edge of the piston skirt are determined by the design constraints, where the component can extend over any axial length whatever between the two edges, and it is also conceivable that the lower edge of the component extends as far as the upper edge of the piston skirt or even seats against it.
To further increase stability it is even conceivable that the lower edge of the component is also welded to the upper edge of the piston skirt.
In a further development of the invention, the component has an inward facing flange, which extends at least over a partial area of the open-bottomed cooling channel. The forces impinging on the surface guidance area of the component are absorbed by this inward facing flange so that stability is thereby further increased. A side effect of this inward facing flange can be seen in the fact that the open-bottomed cooling channel is at least partially closed so that the available cooling medium collects in the cooling channel and contributes to the cooling of the piston crown. With this arrangement, the inward facing flange can cover the open-bottomed cooling channel completely, thereby creating a closed cooling channel. As an alternative, the inward facing flange can only partially cover the open-bottomed cooling channel so that the cooling channel remains at least partially open at the bottom. This has the advantage that cooling medium can continue to flow into and out of the cooling channel through the open areas.
In a further development of the invention, the downstanding flange of the component (in the direction of the upper edge of the piston skirt) and the inward facing flange are positioned at an angle, specifically at an approximate right angle, to each other. This means that the component with its flange is manufactured in such a way that the latter are positioned approximately at right angles to each other. This component can, for example, be manufactured by casting, although other manufacturing methods are also conceivable. For example, both flanges can be manufactured as stamped or formed components and then welded together.
In a further development of the invention, the flanges are either of the same thickness or are of different thicknesses. The thicknesses to be employed are determined specifically by the load on the component, that is, in order to produce the desired stability, the flanges must be sized in such a way that they are able to absorb and dissipate the forces that are generated.
In a further development of the invention, the component is located at least in the area above the piston skirt. Since the piston skirts have so far assumed the task of guiding the cooling channel piston and the component is intended to increase the surface guidance area, it is advantageously located above the piston skirt, viewed in the direction of motion of the cooling channel piston. This means that the component extends in the area between the lower edge of the piston ring belt and the upper edge of the piston skirt and at least within the area between the longitudinal edge of the piston skirt (viewed in the direction of motion of the piston), where it is also conceivable that the component projects beyond the longitudinal edges of the piston skirt.
In a further development of the invention, the component consists of at least two halves which are held in position in the area of the ring-shaped recess and are welded below the piston ring belt, as part of which the abutting portions specifically are welded together. The result is a component that is rigidly attached to the cooling channel piston, which increases the surface guidance area and can absorb the forces introduced there. The inward facing flanges can, as also in the case of the previously described embodiments, seat against the body of the cooling channel piston, although this is not absolutely necessary, so that an opening can remain between the circumferential edge of the inward facing flange and the body of the cooling channel piston. Manufacturing the component from at least two halves has the advantage that after the circumferential ring-shaped recess and the cooling channel have been introduced, they can be placed around the cooling channel piston in the area of the recess so that the welding procedure can then be carried out to join the component to the piston ring belt.